The autopilot during a Single Channel ILS approach should be disengaged at the final decision altitude. This is the point where the pilot must decide whether to continue for a landing or execute a missed approach if the visual reference is not obtained.
The question relates to the operation of the autopilot during a Single Channel ILS approach.
According to standard aviation procedures, the autopilot should be disengaged at the final decision altitude (FDA) or decision height (DH) if the approach is not continued to a landing.
The FDA/DH is the specified altitude or height in a precision instrument approach at which a missed approach must be initiated if the required visual reference to continue the approach to land has not been established.
Disengaging the autopilot before the approach briefing or once established on the localizer and glideslope is not necessary or recommended, as the autopilot assists the pilot in maintaining the correct flight path.
Additionally, disengaging at the missed approach point may actually be too late, as the pilot should be prepared to manually fly the missed approach procedure from the final decision altitude.